Learn French: J'ai décidé de démonter cette voiture classique.

In French, certain verbs need a connecting preposition like de or à before a following infinitive. The verb décider requires de when you say you decide to do something (décider de faire quelque chose). It simply acts as a bridge between the two verbs.

Is de the only preposition used to connect verbs? How do I know which one to use?

Some verbs take de (like décider de or oublier de), some take à (like apprendre à), and some connect directly with no preposition at all (like vouloir or pouvoir). There isn't a strict rule to guess them, so it is best to memorize the preposition as part of the verb itself.

What does the prefix dé- do in the verb démonter?

It reverses the action of the base verb. The verb monter can mean to assemble or put together. By adding the prefix dé-, it becomes démonter, which means to take apart or dismantle.

Why do we use cette here instead of ce?